This invention relates to a method of obtaining a gel-forming protein product from oil seeds that may or may not be defatted.
Gel-forming products containing vegetable proteins are used in foodstuffs for human consumption, for example, in dietary and baby foods, in meat products, such as ham and chicken, and as a binding agent in meat emulsions.
It is known that oil seeds such as soy beans are used as raw materials for such products. Oil seeds, such as soy beans, ground nuts, sunflower seeds, rape seeds and the like, are made up of cells the walls of which can be described as the polysaccharide fraction. The cell content consists mainly of oil, protein and soluble sugars and minor constituents, such as minerals, lecithines, enzymes and many other substances, that together ensure that the seed can germinate and develop into a plant.
According to the known methods of obtaining a gel-forming product from these raw materials, the proteins therein are separated from the oils, the polysaccharide fraction and the soluble sugars and are subsequently subjected to a heat treatment in aqueous solution whereby bonds are formed in the native proteins which lead to gel formation.
An example of a conventional process for obtaining the protein is taken from Belgian Pat. No. 707 302 (Fuji Oil).
The soy beans are flaked and then--possibly after having been defatted by extraction with organic solvents--the flakes extracted with water as a result of which the native proteins dissolve together with the other water soluble constituents. The aqueous extract is separated from the insolubles. Subsequently, the solution is acidified to the isoelectric point as a result of which the proteins precipitate and can be separated from the constituents remaining in solution. The proteins are then redissolved by neutralization in aqueous medium. By heating the aqueous solution, for example to 100.degree. C., the native protein is converted into a gel-forming product. The so-called soy isolate thus obtained has good water absorption, emulsifying and gel-forming properties. A disadvantage of this method, however, is that the method is cumbersome and expensive. Large facilities for the neutralisation and treatment of effluent are required and, besides, the yield is poor. Less than two-third of the protein present in the raw material is obtained as gel-forming protein.
Surprisingly I have now found that it is possible to obtain a product that forms a good gel by means of a heat treatment whereby it is not essential to separate the proteins from the other constituents beforehand. I have found that the polysaccharide fraction impedes the conversion of native protein to gel-forming protein, if this fraction is intimately mixed with the proteins as occurs on heating the material obtained by converting oil seeds into meal or flour.
According to the present invention I provide a method for obtaining a gel-forming protein product from either defatted or non-defatted oil seeds or products derived therefrom which contain protein, carbohydrates and oils whereby the proteins are subjected to one or more thermal treatments above 50.degree. C. in water while maintained in a state of separation from the polysaccharide fraction, the duration of the thermal treatment being sufficient to convert proteins present into their gel-forming state.
By the use of this method the precipitation of the proteins by acidification and the subsequent neutralization of the precipitated proteins are no longer required.